This research project will conclusively demonstrate the effects of a high fat diet on the induction of mammary cancers in 3 strains of rats. The possible co-carcinogenic effect of a high fat diet in mammary cancer induction by a chemical carcinogen will be defined. The possibility that high dietary fat alters the susceptibility of the mammary gland to carcinogenesis as related to the age of the host, the rate of mammary cell proliferation and hormone biosynthesis will be investigated by studying whether a fat diet may increase the incidence of mammary cancer in post-pubertal rats; by examining whether a high fat diet accelerates the rate of DNA synthesis and cell proliferation; and by measuring the biosynthesis of steroid and polypeptide hormones. The possible relationship between increased hormone production and increased rate of mammary cell proliferation in rats ingesting a high fat diet may be delineated. A comparison of the efficacy of polyunsaturated and unsaturated fat in their co-carcinogenic effect may lead to the identification of the type of fatty acid in the high-fat diet causing enhancement of mammary tumorigenesis. Or the possibility that the amount of dietary fat consumed, rather than the specific type of dietary fat, may play a critical role in influencing the induction of mammary carcinogenesis may be ascertained.